Development of Ultra-high Density Three-dimensional Optical Data storage System

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Optical data storage systems, such as CD and DVD, are now widely used. However, capacity of such currently available storage systems are not enough for recording movies in a high-quality even the storage densities are almost reaching to the theoretical limit. Accordingly a new data storage system is required. We have developed three-dimensional (3D) optical data storage system using silica as recording material, and clarified the following points :1. By irradiation of picosecond or femtosecond single pulse, a change in reflactive index is induced in a small domain (reffered as "bit") through a multiphoton process. Using such an effect, a three-dimensional data storage system can be constructed.2. The time-period to generate a bit was about 400 ps.3. A small hollow was generated at the center of the bit.4. The bits are thermally stable extremely ; by annealing at 1150 degree no change was induced in optical microscope image.5. The bits showed a specific luminescence spectra. The luminescence intensity was reduced by thermal annealing ; by annealing at 500 degree the luminescent property was almost lost.6. For multi-layer recorded samples, each layer was independently read by both transmission and luminescence images.7. In the other materials such as PMMA, the same effect was found.